1. Field of Invention
In general, the present invention relates to an image sensing device. In particular, the present invention relates to an automatic tracking/image sensing device typically mounted on an elevator, a car or the like for sensing the image of an image sensing target object while tracking the image sensing object.
2. Background of the Invention
The conventional automatic tracking/image sensing device 1 has a typical configuration shown in FIG. 1.
The automatic tracking/image sensing device 1 shown in FIG. 1 comprises: a lens barrel 2; an image sensing device 3 attached to the lens barrel 2; a video signal processing means 4; an object position detecting means 5 for recognizing an image sensing target object on a screen created by a video signal generated by the video signal processing means 4, detecting the position thereof and calculating a moving direction and angle toward the center of the screen; and a lens barrel posture controlling means 6 for moving the lens barrel 2 in accordance with the moving direction and angle detected by the object position detecting means 5.
With the automatic tracking/image sensing device 1 having the configuration described above, an image of an image sensing object is created on a light receiving surface of the image sensing device 3 by means of a lens of the lens barrel 2. In other words, the image sensing device 3 outputs picture element data of the image sensing object. Then, the video signal processing means 4 generates a video signal S1 constituting a screen based pieces of the picture element data output by the image sensing device 3 and outputs the video signal S1 to an external monitor unit or the like.
Here, receiving the video signal S1 generated by the video signal processing means 4, the object position detecting means 5 recognizes the image sensing object on the screen and detects the position thereof. Then, the object position detecting means 5 computes the value of the positional deviation from the center of the screen, that is, the moving direction and angle to the center of the screen. Finally, the object position detecting means 5 outputs a control signal S2 representing the positional deviation.
Receiving the control signal S2 representing the positional deviation generated by the object position detecting means 5, the lens barrel posture controlling means 6 moves the lens barrel 2 in the horizontal and vertical directions. As a result, the image of the image sensing target object moves to the center of the screen photographed by the image sensing device 3 in the so-called automatic tracking operation.
In the automatic tracking/image sensing device 1 with the configuration described above, the lens barrel posture controlling means 6 employs a direct current or stepping motor as a driving means for moving the lens barrel 2 in the horizontal and vertical directions in order to control the posture of the lens barrel 2 through a reduction gear mechanism such as a gear transmission mechanism.
For this reason, the accuracy of the positioning of the lens barrel 2 by the posture control inevitably decreases due to a backlash of a toothed wheel of the reduction gear mechanism.
In addition, particularly in the case of a stepping motor, the stop position of the driving shaft thereof is determined for each step. As a result, the posture control's positional resolution of the lens barrel 2 deteriorates and the response speed decreases.
On the other hand, it is necessary to increase the response speed and enhance the positioning accuracy in order to correct deflection resulting from the posture control which is carried out while the automatic tracking is being performed. It is difficult, however, to correct such deflection in the configuration described above.
On top of that, since the configuration described above includes a reduction gear mechanism, the configuration of the lens barrel posture controlling means 6 becomes complex, giving rise to a problem that the automatic tracking/image sensing device inevitably becomes large in size.
As another example, there is a configuration for correcting deflection resulting from the posture control wherein the lens barrel 2 is supported by a gimbals mechanism, being driven directly by a driving means and a deflection detecting sensor provided on the lens barrel 2 detects the magnitude of the deflection. Since the deflection detecting sensor is relatively large in size, however, the moving part of the lens barrel 2 also inevitably increases in size as well. As a result, such a configuration works against any attempt made to reduce the size of the lens barrel 2.
In still another configuration, a deflection detecting sensor is provided on the stationary portion of the image sensing device. In this case, however, a sensor for detecting the angular speed of the lens barrel itself is required, giving rise to another problem that the configuration inevitably becomes complicated.